1. Field of Invention
This invention relates broadly to seals which prevent entrance of contaminants into various types of machinery, and more particularly, to seals between a rotatable shaft and a housing.
2. Prior Art
Many industries require the use of machines in which a rotatable shaft is contained by a housing. The housing usually contains lubricated bearings and sometimes additional attachments to the shaft such as turbine blades or gears. There are many types of seals provided between a shaft and a housing so as to prevent the leakage of lubricants from the housing and/or to prevent external contaminants from entering the housing along the shaft. In high speed operations of such rotating shaft mechanisms, contaminants to the internal lubricant result in increased wear, costly replacement of parts and, consequently, down time for the mechanism.
It is known to provide a sealing ring assembly comprising a first ring fixed to the housing and a second ring exterior to the housing and fixed to rotate with the shaft. Such an assembly is disclosed by U.S. Pat. No. 4,002,479, invented by David C. Orlowski and issued on May 10, 1977. In Orlowski, the first ring is held fixed to the housing by an o-ring and has an annular recess which matingly receives an annular flange of the rotating second member so as to allow free rotation without contact between the flange and the recess. The contaminants are theoretically discharged through an opening in the bottom of the recess in the first ring. The second ring is secured to the shaft by an o-ring. This arrangement has failed to prevent certain contaminants from entering the housing. An example of such a problem arises in the steam turbine industry, where such a seal is subject to an environment of steam, itself a contaminant, and also particles carried in the steam. In such an environment, steam easily penetrates the crevices between the first and second rings, condenses and is carried into the housing along the rotating shaft. An even greater contamination problem is created when the shaft is at rest and contaminants are allowed to build up and travel along the surfaces of the static rings to the static shaft which provides less frictional resistance to the contaminants than a moving shaft. A further problem arises when the o-rings or the sealing rings must be changed, which requires extensive down time while other components are removed in order to allow the sealing rings to be removed from the shaft.